1. Field of the Invention
The present invention in general relates to the copying of digital data from electro-magnetic media, including disc and tape media. In particular, the present invention pertains to a system for the blind copying of data regardless of format or encoding scheme.
2. Prior Art
In the field of magnetic data copying, particularly concerning disc media, the quality of the reproduced data is of prime importance. Many factors contribute to the degredation of the copy, including synchronization errors inherent in the drive units if mechanical synchronization is used.
One common method of copying data fields which requires no mechanical synchronization is to store the entire decoded data field in a buffer memory and then to serially write the data from the buffer memory onto a duplicate disc. The method of duplicating data on disc media thus requires that both the master and the duplicate disc have pre-recorded format information particular to each manufacturer. Generally, the format used requires up to fifty percent of the disc capacity for identification field, address marks and data gaps. Accordingly, the copying of data requires a "prerecorded" or formatted disc and does not allow true "blind copying". The data fields can be copied, but not the format. Currently, most commercially available computer systems are capable of data field copying.
As previously mentioned, another method used to copy data requires electro-mechanical synchronization, so that the spindles of all slave drives are synchronized with the index of master. This method requires no buffer storage, but does introduce synchronization errors and requires expensive precision drives.
Another attempt to continuously duplicate data directly is shown in U.S. Pat. No. 3,805,284 to Coon, Jr., et al. U.S. Pat. No. 3,805,284 teaches an apparatus and method for duplicating and verifying the data utilizing a read/write data synchronizer. The Coons apparatus provides bit to bit data verification via a Data Verifier before being read out. Although U.S. Pat. No. 3,805,284 makes reference to disc media, the apparatus disclosed is more appropriate for transferring data from tape to tape as it is not appropriate for transferring the data from disc to disc as is necessary for the blind copying of disc media. The reason that the device disclosed in U.S. Pat. No. 3,805,284 is not appropriate for disc to disc blind copying is that the device requires a separate read head verifier downstream from the information being copied. Also, the synchronizer works by varying the speed of the drive motors. It thus requires multiple heads and synchronized drives. Although U.S. Pat. No. 3,805,284 made an attempt to continuously duplicate data, the use of a synchronizer approach inherently introduces errors in the copies made thereby and requires considerable drive modification.
The copying of disc information without regard to format and encoding schemes (blind copying) necessitates having a means for insuring that the digital data is written precisely as it was read. Instead of synchronizing the drive units or verifying the data downstream, a better system would provide an electronic clocking mechanism which is governed by the read data itself and an electronically timed buffer output. The present invention provides such a system by utilizing a phase-locked oscillator, buffer memory and a fixed clock. The invention thus eliminates the necessity to encode/decode data, eliminates synchronization errors, utilizes standard drive units and heads, eliminates extra verifying heads and yet provides high quality, continuous high speed copying of data particularly applicable to flexible disc media. While the present invention particularly relates to flexible disc media, due to its universal character, other electro-magnetic media such as optical discs, rigid discs, or tape could also be copied using the system. Additionally, different sized discs could be copied and converted, such as from 51/4" to 8" disc, and likewise from 8" to 51/4". The copying process could also cross media such as from tape to disc, and disc to tape just as easily since the data is timed by the read data itself.